Nowadays, it has been proved that gallium nitride-based (GaN-based) semiconductor material has potential for the commercial applications such as the backlight module of LCD, optical storage system, high frequency and high power microwave electronic device, where sapphire substrate is mainly used as substrate for the epitaxial growth of GaN-based semiconductor material. However, the fabrication cost of nitride light-emitting diodes is much higher than other illuminating devices, and sapphire substrates for growth of nitride have shortcomings such as poor thermal conductivity which seriously affects the lifespan of the nitride light-emitting diodes. Therefore, replacing the current sapphire substrate with a lower-cost and high thermal conductive substrate is suggested. Due to several advantages of silicon substrates such as high thermal conductivity, high electrical conductivity, ability to be cut easily and low cost, light-emitting diode fabricated over a silicon substrate is developed in recent years.
Nevertheless, production yield rate of large-sized nitride semiconductor structures fabricated over silicon substrates is low, it is difficult to significantly lower the cost of the devices accordingly. The main factor for affecting the yield rate of large-sized nitride semiconductor structures is thermal expansion mismatch and lattice mismatch between the nitride semiconductor layer and the silicon substrate. Thermal expansion mismatch and lattice mismatch between the nitride semiconductor layer and the silicon substrate cause difficulty in stress release and increase defect density, and thus it may cause the nitride semiconductor structures to have considerable cracks and tensile stress. In other words, the nitride semiconductor structures may crack easily. Moreover, the chip bonding equipment and the laser ablation equipment utilized to lift-off substrate are expensive, and the yield rate of the chip bonding process and the laser ablation process is low. Therefore, how to form a GaN epitaxy structure on a silicon substrate to significantly enhance the yield rate of the chip bonding process without the use of laser ablation, becomes an essential topic in the field.